Method of controlling leachable mercury in lamps

ABSTRACT

A method for inhibiting mercury from leaching from a land-filled arc discharge lamp containing a quantity of elemental mercury at least partially convertible to soluble mercury, provides for including within the lamp a quantity of a non-metallic copper-containing compound and an ingredient X, said ingredient X including a noble metal or a noble metal compound selected from the group consisting of silver and compounds of silver, gold and platinum, and a lamp containing same. The inhibiting compound is preferably included with the basing cement.

TECHNICAL FIELD

This invention relates to mercury vapor discharge lamps and moreparticularly to fluorescent lamps. Still more particularly it relates tolamps that can be landfilled without leaching potentially damagingmercury into the environment.

BACKGROUND ART

During the manufacture of a fluorescent lamp, as well as other types ofarc discharge lamps, a quantity of elemental mercury is sealed withinthe lamp envelope. It is known that in operation some of the elementalmercury contained in these lamps can be converted to a mercuric oxide ora mercury salt. This is true in fluorescent lamps in particular. In suchlamps most of this mercury adheres to the phosphor coating depositedupon the inside wall of the lamp envelope, leaving only a small portionof the mercury in the form of mercury vapor. After the alkaline earthmetal oxides coating the lamp electrodes are volatilized, the oxidesdecompose in the discharge space, and the freed oxygen converts some ofthis elemental mercury to a salt or compound such as the above-mentionedmercuric oxide (HgO) which is water soluble.

There is a growing concern that a waste stream resulting from thedisposal of arc discharge lamps such as fluorescent lamps may leachexcessive amounts of soluble mercury into the environment. One method ofmeasuring the amount of soluble mercury, which may leach from the wastestream resulting from the disposal of fluorescent lamps, is described inthe Toxicity Characteristic Leaching Procedure (TCLP) prescribed onpages 26987-26998 of volume 55, number 126 of the Jun. 29, 1990 issue ofthe Federal Register. According to the procedure, the lamp being testedis pulverized into granules having a surface area per gram of materialequal to or greater than 3.1 cm² or having a particle size smaller than1 cm in its narrowest dimension. Following pulverization, the granulesare subjected to a sodium acetate buffer solution having a pH ofapproximately 4.93 and having a weight twenty times the weight of thegranules.

At the present time, the Environmental Protection Agency defines amaximum concentration level for mercury at 0.2 milligram leachablemercury per liter extract fluid when the TCLP is applied. According topresent standards, a fluorescent lamp is considered nonleachable, andthus available for conventional landfill deposition, when less than 0.2milligram per liter of leachable mercury results from a TCLP extraction.

Various methods have been proposed which attempt to treat or processburned-out discharge lamps or scrap lamp exhaust tubing containingmercury in order to reclaim the mercury and thereby reduce the amount ofmercury-contaminated scrap. These methods are summarized as backgroundin U.S. Pat. No. 5,229,686 and U.S. Pat. No. 5,229,687, which describemethods by which to render a mercury vapor lamp nonleaching upondisposal without the use of expensive treatment processes to reclaim themercury. The method of U.S. Pat. No. 5,229,686 employs a chemical agent,enclosed within the lamp, suitable for chemically combining asubstantial portion of the soluble mercury as a sparingly soluble saltwhen the lamp is pulverized as a result of disposal. The method of U.S.Pat. No. 5,229,687 employs a chemical agent, enclosed within the lamp,suitable for electrochemically reducing a substantial portion of thesoluble mercury to elemental mercury, again when the lamp is pulverizedduring disposal. Preferably, this chemical agent is an element which hasan electrode potential for oxidation reactions higher than mercury butwhich is not sufficiently active to displace hydrogen from acidicaqueous solutions. In a preferred embodiment, the chemical agent issealed within an enclosure (e.g., glass), which is rupturable uponpulverization of the lamp. In another embodiment, the chemical agent ismixed with the basing cement used to secure the lamp bases to the glassenvelope. The chemical agent acts to reduce soluble mercury producedduring lamp operation to elemental mercury, which is not leachable asmeasured by the TCLP.

The chemical agent used in '687 may be used in various forms, e.g., as apowder, dust, wire mesh, or metallic foil. The amount or size of thechemical agent is directly related to the surface area and surfacecondition, finely divided metallic powders being preferred over a solidmass because of their relatively large effective surface areas. Becauseof their availability and inexpensive cost, iron and copper, in the formof a powder or dust, are preferred. The amount of chemical agent presentshould be sufficient to electrochemically reduce the amount of solublemercury within the lamp which is leached at the time of disposal to lessthan 0.2 milligram per liter of an aqueous acid solution such as asodium acetate buffer solution as prescribed in the TCLP.

However, there are several disadvantages to the methods described inU.S. Pat. No. 5,229,686 and '687. In regard to '686, the quantity ofchemical agent required to chemically combine nearly all of the mercurywithin a fluorescent lamp may be so large as to be inconvenient orimpossible to contain within a standard lamp envelope. In regard to'687, the metallic copper or iron reduces the amount of leachablemercury via a surface redox reaction between adsorbed mercury ions andzero-valent metal atoms. In order for this reaction to occur, thedissolved ionic mercury must first find its way to and become adsorbedupon the metal surface. Thus, the effectiveness of a metallic element asa means of reducing leachable mercury will ultimately be limited by therates at which mercury ions diffuse to the metal surface and becomeadsorbed thereon. A means of reducing leachable mercury that did notdepend upon the chance contact between dissolved mercury ions and ametal surface followed by the adsorption of the mercury upon thatsurface would be likely to be more efficient and, therefore, preferable.

It may also be difficult or impossible to incorporate a sufficientlylarge quantity of a finely divided metal within a fluorescent lamp, themore so the smaller or more compact the lamp. In a small lamp, the onlyconvenient way to introduce the metal may be as a component of thebasing cement. However, the electrical conductivity of the metal mayprevent its incorporation into the basing cement since the cement mayeasily come into contact with internal electrical leads. On the otherhand, electrically insulating materials might easily be added to thebasing cement in addition to or in place of the normal CaCO₃ cementfiller without risk of creating electrical short circuits within thelamp.

In U.S. Pat. No. 5,736,813, it is disclosed that “the formation ofleachable mercury upon disposal or during TCLP testing of mercury vapordischarge lamps is substantially prevented by incorporation of a pHcontrol agent in the lamp structure or in the test solution to provide apH of about 5.5 to 6.5.” A low pressure mercury discharge lamp isclaimed which includes about 5-15 grams of a pH control agent (generallya water-soluble base) which, it is suggested, is sufficient tosubstantially prevent formation of ferric and cupric compounds whichoxidize elemental mercury to a soluble form. The primary disadvantage ofthis method of reducing mercury leaching is that it may be difficult or,depending upon the lamp type, practically impossible to package therelatively large amounts of the required pH control agent (5-15 grams)within the structure of a typical mercury vapor lamp.

Recently, an improved mercury vapor discharge lamp was described inwhich an effective amount of a nonmetallic copper-containing compoundwhich, when the lamp is pulverized to granules and subjected to asuitable aqueous acid solution, dissolves in the acid solution,resulting in a concentration of extracted mercury less than 0.2 mg perliter of solution. The effective amount of soluble copper is relativelysmall (between 0.1 and 4 mg per gram of total lamp weight, dependingupon lamp type and size, total mercury loading, etc.). However, copperin the environment, although relatively harmless, may be toxic tocertain marine invertebrates. In order to eliminate the possibility ofdamage to ecological systems, the EPA has placed a limit of 25 mg/L forcopper levels in discharges from nonferrous operations to lakes andstreams. It is desirable, therefore, to minimize the amount of solublecopper, which is effective with respect to the control of mercuryleaching. Further, the smaller the quantity of nonmetalliccopper-containing compound, the more easily it will be to incorporatewithin the lamp.

The use of so-called noble metals and metal salts has also beensuggested for the control of mercury leaching in fluorescent lamps. U.S.Pat. No. 6,515,421 describes a method and apparatus for preventing theformation of leachable mercury in mercury arc vapor discharge lamps,which comprises coating at least one of the metallic components of thelamp with at least one noble metal coating (typically silver orpalladium). A method and apparatus for preventing the formation ofleachable mercury in mercury arc vapor discharge lamps which comprisesproviding in the lamp structure an effective amount of a silver salt,gold salt, or combination thereof, is described in U.S. Published patentapplication No. 2002/0190646 A1. While these methods may be effectivefor the control of leachable mercury, they are generally not practicaldue to the relatively high costs of the noble metals and metal salts.However, the use of such noble metals or metal salts might becomepractical if a relatively inexpensive means were found to substantiallyreduce the amounts of these substances which are required to effectivelyreduce or control mercury leaching.

DISCLOSURE OF INVENTION

It is, therefore, an object of the invention to obviate thedisadvantages of the prior art.

It is another object of the invention to enhance the disposability ofmercury-containing discharge lamps.

Yet another object of the invention is the provision of a method forcontrolling leachable mercury in discharge lamps.

These object are accomplished, in one aspect of the invention, by amethod for inhibiting mercury from leaching from a land-filled arcdischarge lamp that contains a quantity of elemental mercury at leastpartially convertible to soluble mercury, the method comprisingincluding within the lamp a quantity of a non-metallic copper-containingcompound and an ingredient X, said ingredient X including a noble metalor noble metal compound selected from the group consisting of silver andcompounds of silver, platinum and gold.

The combination of the non-metallic copper-containing compound and thenoble metal or noble metal compound provides a method that is effective,inexpensive and easy to apply.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph providing test results with various amounts of silveraddition;

FIG. 2 is a graph providing test results with various amounts of ioniccopper addition;

FIG. 3 is a diagrammatic view of a lamp employing an embodiment of theinvention; and

FIG. 4 is a view similar to FIG. 3 of an alternate embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

For a better understanding of the present invention, together with otherand further objects, advantages and capabilities thereof, reference ismade to the following disclosure and appended claims taken inconjunction with the above-described drawings.

Referring now to the invention with greater particularity, it has beendiscovered that a relatively small amount of a soluble non-metalliccopper-containing compound used in combination with a small quantity ofmetallic silver or a compound of silver, platinum, or gold in theToxicity Characteristic Leaching Procedure applied to a mercury vapordischarge lamp containing a quantity of mercury that is at leastpartially convertible to soluble mercury may be much more effective inpreventing mercury leaching than either the copper-containing compoundor the metallic silver or compound of silver, platinum, or gold usedalone. Thus, as a result of the presence of a small amount of metallicsilver or a compound of silver, platinum, or gold, concentrations ofextracted mercury much less than 0.2 mg per liter of solution may beobtained with quantities of soluble copper-containing compoundssubstantially smaller than would be required to achieve the sameextracted mercury concentrations in the absence of the metallic silveror compound of silver, platinum, or gold. Conversely, as a result of thepresence of a relatively small amount of a soluble copper-containingcompound, concentrations of extracted mercury much less than 0.2 mg perliter of solution may be obtained with quantities of metallic silver orof compounds of silver, platinum, or gold substantially smaller thanwould be required to achieve the same extracted mercury concentrationsin the absence of the dissolved copper compound. Various aspects of thisinvention are presented in the following examples.

EXAMPLE 1

A series of four TCLP tests were carried out with commercial 32WT8fluorescent lamps manufactured without metallic mercury but with 6 mg ofionic mercury (as HgO) soluble in the TCLP extraction fluid. Noadditives were used in one of the tests. However, each of the otherthree tests included 50 mg of copper as the compound copper dihydroxidecarbonate (CDC), 4 mg (4×10⁻⁵ mole) of finely divided metallic silver(with most particles in the 0.5-1.0 micron range), or a combination ofthe two. The TCLP test results (leached mercury concentration in unitsof mg per liter of extraction fluid) are listed in Table I below for T8lamps with 6 mg soluble Hg²⁺.

TCLP Results for T8 Lamps without Metallic Hg, with 6 mg Soluble Hg²⁺,and with a Soluble Copper-Containing Compound (CDC), Finely Divided(0.5-1.0 Micron) Metallic Silver, a Combination of CDC and FinelyDivided Metallic Silver, or No Additive Added at the Start of the TestTABLE I Cu (as CDC) (mg) Ag (0.5-1.0 micron) (mg) Leached Hg (mg/L) 0 00.82 50 0 0.31 0 4 0.29 50 4 0.05

It is seen that a relatively small amount of a soluble nonmetalliccopper-containing compound used in combination with a small quantity ofmetallic silver in the Toxicity Characteristic Leaching Procedureapplied to a mercury vapor discharge lamp containing a quantity ofmercury that is soluble in the acidic extraction fluid may be much moreeffective in preventing mercury leaching than either thecopper-containing compound or the metallic silver used alone.

EXAMPLE 2

Additional TCLP tests were carried out in the same way as thosedescribed in Ex. 1 except that 4 mg of silver as silver oxide, Ag₂O, wasused rather than metallic silver. As before, tests were performed bothwith and without the presence of 50 mg of copper as CDC. The results ofthese tests, along with those performed without the addition of silveroxide, are compared in Table 2 below.

TCLP Results for T8 Lamps without metallic mercury, with 6 mg SolubleHg²⁺ and with a Soluble Copper-Containing Compound (CDC), Silver Oxide(Ag₂O), a Combination of CDC and Silver Oxide, or No Additive Added atthe Start of the Test. TABLE II Cu (as CDC) (mg) Ag (as Ag₂O) (mg)Leached Hg (mg/L) 0 0 0.82 50 0 0.31 0 4 0.24 50 4 0.07

It is seen that a relatively small amount of a soluble nonmetalliccopper-containing compound used in combination with a small quantity ofsilver oxide in the Toxicity Characteristic Leaching Procedure appliedto a mercury vapor discharge lamp may be much more effective inpreventing mercury leaching than either the copper-containing compoundor the silver compound used alone.

EXAMPLE 3

Additional TCLP tests were carried out in the same way as thosedescribed in Ex. 2 except that 4 mg of silver as silver carbonate,Ag₂CO₃, was used rather than silver oxide. As before, tests wereperformed both with and without the presence of 50 mg of copper as CDC.The results of these tests, along with those performed without theaddition of silver carbonate, are compared in Table 3 below.

TCLP Results for T8 Lamps without Metallic Hg, with 6 mg Soluble Hg²⁺and with a Soluble Copper-Containing Compound (CDC), Silver Carbonate(Ag₂CO₃), a Combination of CDC and Silver Carbonate, or No AdditiveAdded at the Start of the Test. TABLE III Cu (as CDC) (mg) Ag (asAg₂CO₃) (mg) Leached Hg (mg/L) 0 0 0.82 50 0 0.31 0 4 0.24 50 4 0.12

As in the preceding example, it is seen that a relatively small amountof a soluble nonmetallic copper-containing compound used in combinationwith a small quantity of a silver compound in the ToxicityCharacteristic Leaching Procedure applied to a mercury vapor dischargelamp may be much more effective in preventing mercury leaching thaneither the copper-containing compound or the silver compound used alone.

EXAMPLE 4

Additional TCLP tests were carried out in the same way as thosedescribed in the preceding examples except that 4 mg of silver as silverchloride, AgCl, was used rather than metallic silver or another silvercompound. As before, tests were performed both with and without thepresence of 50 mg of copper as CDC. The results of these tests, alongwith those performed without the addition of silver chloride, arecompared in Table 4 below.

TCLP Results for T8 Lamps without Metallic Hg, with 6 mg Soluble Hg²⁺and with a Soluble Copper-Containing Compound (CDC), Silver Chloride(AgCl), a Combination of CDC and Silver Chloride, or No Additive Addedat the Start of the Test TABLE IV Cu (as CDC) (mg) Ag (as AgCl) (mg)Leached Hg (mg/L) 0 0 0.82 50 0 0.31 0 4 0.21 50 4 0.05

As in the preceding examples, it is seen that a relatively small amountof a soluble nonmetallic copper-containing compound used in combinationwith a small quantity of a silver compound in the ToxicityCharacteristic Leaching Procedure applied to a mercury vapor dischargelamp may be much more effective in preventing mercury leaching thaneither the copper-containing compound or the silver compound used alone.

EXAMPLE

Additional TCLP tests were carried out in the same way as thosedescribed in the preceding example except that 7 mg (4×10⁻⁵ mole) ofgold as gold chloride, AuCl₃, was used rather than silver chloride. Asbefore, tests were performed both with and without the presence of 50 mgof copper as CDC. The results of these tests, along with those performedwithout the addition of gold chloride, are compared in Table 5 below.

TCLP Results for T8 Lamps without Metallic Hg, with 6 mg Soluble Hg²⁺,and with a Soluble Copper-Containing Compound (CDC), Gold Chloride(AuCl₃), a Combination of CDC and Gold Chloride, or No Additive Added atthe Start of the Test. TABLE V Cu (as CDC) (mg) Au (as AuCl₃) (mg)Leached Hg (mg/L) 0 0 0.82 50 0 0.31 0 7 0.51 50 7 0.10

As in the preceding examples, it is seen that a relatively small amountof a soluble nonmetallic copper-containing compound used in combinationwith a small quantity of a gold compound in the Toxicity CharacteristicLeaching Procedure applied to a mercury vapor discharge lamp may be muchmore effective in preventing mercury leaching than either thecopper-containing compound or the gold compound used alone.

EXAMPLE 6

Additional TCLP tests were carried out in the same way as thosedescribed in the preceding example except that 8 mg (4×10⁻⁵ mole) ofplatinum as platinum chloride, PtCl₂, was used rather than silverchloride. As before, tests were performed both with and without thepresence of 50 mg of copper as CDC. The results of these tests, alongwith those performed without the addition of gold chloride, are comparedin Table 6 below.

TCLP Results for T8 Lamps without Metallic Hg, with 6 mg Soluble Hg²⁺and with a Soluble Copper-Containing Compound (CDC), Platinum Chloride(PtCl₂), a Combination of CDC and Platinum Chloride, or No AdditiveAdded at the Start of the Test. TABLE VI Cu (as CDC) (mg) Pt (as PtCl₂)(mg) Leached Hg (mg/L) 0 0 0.82 50 0 0.31 0 8 0.52 50 8 0.03

As in the preceding examples, it is seen that a relatively small amountof a soluble nonmetallic copper-containing compound used in combinationwith a small quantity of a platinum compound in the ToxicityCharacteristic Leaching Procedure applied to a mercury vapor dischargelamp may be much more effective in preventing mercury leaching thaneither the copper-containing compound or the platinum compound usedalone.

EXAMPLE 7

Additional TCLP tests were carried out in the same way as were thosedescribed in Ex. 1. However, in this case, two series of tests wereconducted with increasing amounts of finely divided metallic silver(with most particles in the 0.5-1.0 micron range). 50 mg of copper asthe compound copper dihydroxide carbonate (CDC) was included in oneseries of tests, while the other series of tests were carried outwithout the addition of a soluble copper-containing compound. Theresults of these TCLP tests (extracted mercury concentrations obtainedwith and without the addition of CDC) are plotted in FIG. 1 vs. theamount of metallic silver that was included in each test. As indicated,the amount of metallic silver needed to reduce the leachable mercuryconcentration to below the 0.2 mg/l threshold level in the presence ofonly 50 mg of soluble copper is a small fraction of that required in theabsence of the soluble copper compound.

EXAMPLE 8

Three additional series of TCLP tests were carried out similar to thosedescribed in Ex. 7. However, in each of these test series, the amount ofsoluble copper (as CDC) was systematically varied while the amount ofmetallic silver powder was held constant at 0, 3, or 5 mg. The resultsof these TCLP tests (extracted mercury concentrations obtained with theaddition of 0, 3, or 5 mg of 0.5-1.0 micron metallic silver powder) areplotted in FIG. 2 vs. the amount of soluble copper that was included ineach test. As shown, the amount of soluble copper needed to reduce theleachable mercury concentration to below the 0.2 mg/l threshold leveldecreases rapidly with the addition of very small amounts of metallicsilver.

EXAMPLE 9

Additional TCLP tests were carried out with commercial 32WT8 fluorescentlamps manufactured without metallic mercury but with 8.5 mg of ionicmercury (as HgO) soluble in the TCLP extraction fluid. Several testswere run with lamps having each of three different basing cementcompositions. The basing cement was a typical cement comprising an inertfiller of CaCO₃ and a polymer such as phenol formaldehyde. Type 1 cementwas formulated in the normal way except that it contained about 34 mg ofsilver as Ag₂CO₃. Type 2 cement was formulated in the normal way exceptthat it contained about 250 mg of copper (as CDC, substituted for about25% of the CaCO₃ cement filler material). Type 3 cement was identical totype 2, except that it contained about 17 mg of silver (as Ag₂CO₃) inaddition to about 250 mg of copper (as CDC). The averaged TCLP resultsobtained with lamps containing each of these three cement compositionsare listed in Table 7 below.

FIG. 3 illustrates diagrammatically a portion of a fluorescent lamp 10having an envelope 12 sealed at one end 14. Two electrical lead-ins 16,18 are sealed into the end 14 and interior of the envelope mount afilamentary cathode 20. Exteriorly of the envelope the lead-ins projectfrom a base 22 for connection to a power source. The base 22 iscup-shaped and sealed to the envelope 12 by a basing cement 24, whichcan be formulated as described above.

TCLP Results for T8 Lamps without Metallic Hg, with 8.5 mg Hg²⁺ (asHgO), and with Type 1, 2, or 3 Basing Cement. TABLE VII Cement Ag (asAg₂CO₃) Cu (as CDC) Leached Type (mg) (mg) Hg (mg/L) 1 34 0 0.21 2 0 2500.20 3 17 250 0.02

It is seen that leachable mercury concentrations at or above theregulatory threshold are obtained with lamps manufactured with cementscontaining about 34 mg of silver or about 250 mg of copper (as compoundssoluble in the TCLP extraction fluid). However, almost no mercury isleached from a lamp manufactured with a cement containing only 17 mg ofsilver (as Ag₂CO₃) combined with only 250 mg of soluble copper (as CDC).

Alternatively, a quantity 25 of the non-metallic copper-containingcompound and the noble metal or noble metal compound can be applied as acoating on the inside surface 26 of the base 22, as is shown in FIG. 4.

While there have been shown and described what are presently consideredto be the preferred embodiments of the invention, it will be apparent tothose skilled in the art that various changes and modifications can bemade herein without departing from the scope of the invention as definedby the appended claims.

1. A method for inhibiting mercury from leaching from a land-filled arcdischarge lamp containing a quantity of elemental mercury at leastpartially convertible to soluble mercury, said method comprising:including within said lamp a quantity of a non-metalliccopper-containing compound and an ingredient X, said ingredient Xincluding a noble metal or noble metal compound selected from the groupconsisting of silver and compounds of silver, gold and platinum.
 2. Themethod of claim 1 wherein said soluble mercury is present as mercuryoxide.
 3. The method of claim 1 wherein said non-metalliccopper-containing comprises copper dihydroxide carbonate.
 4. The methodof claim 1 wherein said ingredient X comprises elemental silver.
 5. Themethod of claim 1 wherein said ingredient X comprises silver oxide asAg₂O.
 6. The method of claim 1 wherein said ingredient X comprisessilver carbonate.
 7. The method of claim 1 wherein said ingredient Xcomprises gold chloride as AuCl₃.
 8. The method of claim 1 wherein saidingredient X comprises platinum chloride as PtCl₂.
 9. The method ofclaim 1 wherein said arc discharge lamp has a base held to said lamp bya basing cement and said non-metallic copper-containing compound andingredient X are included in said basing cement.